Scans confirmed the Welsh international suffered a clean break and the club are hopeful that he will be able to return to action before the end of the season.
Crusaders head coach Iestyn Harris said: “It is obviously a blow to lose Gareth because he has been one of our most consistent performers this season.
“The scans show that it is a clean break so we’re looking at losing him for anything between four to six weeks.
“The break is not as severe as we first thought and there is a really good chance that Gareth will play before the end of the season.
“Gareth is a very determined character and our physio and conditioning team will be working closely with him to ensure that he returns to action fit and healthy.”